<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
    <style>
        main{
            border: 1px silver solid;
            width: 500px;
            height: 500px;
            margin: 0 auto;
        }

        h2{
            border: solid 2px green;
            width: 300px;
            height: 300px;
            margin: 0 80px 100px 150px ;
            /* box-sizing: border-box; */
            box-sizing: content-box;
        }
    </style>

    <main>
        <h2>外边距cesh</h2>
    </main>

</body>
</html>